In recent years, as an in-vitro diagnostic method, there has been proposed a diagnostic method utilizing presentation of color by localized surface plasmon resonance of colloidal gold. For example, in immunochromatography, there is proposed a method using colloidal gold having an antibody fixed thereto, as a tag-labeled particle. According to this method, when an antigen that is an analyte is contained in a specimen, the antigen and the tag-labeled particle are conjugated together to form a composite. The composite develops a moving bed and is captured by an antibody of a determination site. This causes the determination site to exhibit a red color. Whether the antigen is present or absent can be confirmed by confirming whether the determination site exhibits color.
For example, Japanese Patent Laying-Open No. 2009-210505 (PTD 1) discloses an immunological measurement kit aiming at application to immunochromatography. For example, Japanese National Patent Publication No. 2005-533246 (PTD 2) discloses a surface enhanced resonance Raman scattering (SERRS) active bead employed for identifying a target molecule. This bead includes aggregated metallic colloid and at least one SERRS active dye that are encapsulated in a polymer shell.